Process of oxidizing ores.



. greater or less extent in the form of sulfid ores, and these ores for utilization in the arts.

UNITED STATES PATENT OFFICE.

BYRON E. ELDRED, 0F BRONXVILLE, NEW YORK, ASSIGNOR T0 comBus'rIoN UTILITIES COMPANY, or NEW YORK, N. Y.

PROCESS OF OXIDIZING ORES.

No Drawing.

To all whom it may concern:

Be it known that I, BYRON E. ELDREI), a citizen of the United States, residing in Bronxville, in the county of VVestchester and State of New York, have inventeda certain new and useful Process of Oxidizing Ores, of which the following is a specification, This invention relates to processes of oxidizing ores, and consists in a method of froastiug or otherwise oxidizing sulfid ores with dilute gas mixturesyall as more fully hereinafter set forth, matters of novelty be- :ing particularly pointed out in the appended fclaims. p

Most of the heavy metals occur to a must be first roasted or otherwise oxidized. Oxidation of sulfid ores in the air While often difficult to start, and often requiring a relatively high temperature for that purpose, is in general highly exothermic when once begun and, like all highly exothermic reactions, is self-accelerating; with rich ores tending to propagate itself with ever increasing velocitythrough the mass. Heat is liberated not only by the combustion of the sulfur to dioxid or trioxid, but frequently also by the oxidation of the metal base itself, and in some cases, by the union of the oxid produced with the sulfur acid, as in the formation of copper sulfate, lead sulfate, etc. In a confined mass of very rich ore, such as pyrites, copper glance, etc., excessively high temperatures may be, and often are, attained. This development of heat and violence of reaction is detrimental in the extreme when roasting rich ores, and some means of control has long been a desider'atum in the art. The sulfids as a rule are quite fusible andif heated beyond a certain point they melt down, decreasing the surface ex osed to air, tending to inclose portions 0 unchanged sulfids and giving products which are notporous and open in texture,'as is usually desirable, but which are apt to be more in the nature of a sintered mass or matte. Proper roasting of rich sulfid ores is usually regarded as difficult in the extreme, and in the prior art, inventors have gone so far as to convert such richores into poor ores by mixing in inert bodies, such as limestones, silica,

' etc. The adval'ltage gained by checking the rate of combustion and the aecmnulation of heat and thereby attaining a porous, prop- Specification of Letters Patent.

Application filed February 1, 1906.; Serial No. 299,045. I

Patented Aug. 31, 1909.

gangue present is so great as to necessitate the use of extraneous heat to start and maintain the oxidation, with present methods of firing it is also difiicultto secure good results. Control of temperatures is not easy, and the margin of temperature between that degree at which-the ore ignites and that at i which it melts down, is frequently very narrow. The flame atmosphere employed for heatin must of necessity be oxidizing. But all or inary oxidizing flames are extremely short and of limited volume. Therefore in practice in this art, reliance has heretofore been placed mainly on heating by the sensis ble heat of the products of combustion from such a flame, many and ingenious forms of apparatus having been devised to employ such heat to the best advantage. But they all suffer from theradical defect in principle, that sensible heat is given up to the first cooler object encountered. Therefore, charges of ore inv any given furnace are extremely apt to'be overburned in one place and underburned in another. The same difficulties are of course encountered in roasting even rich ore since it is necessary to start combustion with flame heat of some kind. When, as often happens, the gangue of an ore is in itself easily fusible, the difliculties are accentuated! Again, arsenic is very frequently present in sulfid ores and very great care is necessary in the roasting in such cases.

By reason of thesefacts, sulfid roasting is today an uncertain and relatively expensive operation and high-priced skilled labor is generally considered necessary in the art. Butin thepresent invention I have devised a simple, cheap' and easy method of controlling the temperature of the roasting ore, of checking unduly rapid oxidation or facilitating that which is too slow, of regulating the progress of. the reaction with any degree of nicety required, of automatically checking any local tenddncy to become over-heated in any portion of themass of ore being treated and thereby securing evenness of treatment, and of producing \vitlrcertainty any oxidized or other product desired from any given ore.

Rapidity of combustion is a phenomenon depending as much upon the relative mass or concentration of the .oxidantas upon that of the substance oxidized; and it may be varied by varying the concentration of either. For many purposes, as mthis art,

it maybe said that common combustibles,

such as coal, are too concentrated andair itself, so to speak, is also too -'conc'entr'ated; it

be added to complete gives, rise to oxidizing reactions too violent and uncontrollable in their nature. instance, as already stated, 111 the combustion of coal With an excess of airthe result is a' short, small, intensely hot flame, whose area is not sufficient for many purposes. \Vith such-a flame, sensible heat, in lieu of developing heat, m-ustbe'relied uponin treating such a large mass asa few tons of ore; this reliance being further forced by the .fact that direct impingement of such a flame on the orewou ld not be safe because of its inordinate-tern erature. Such a flame is further wasteful 0 fuel as well as inefiicient.

I have discovered that the difliculties hitherto attending the practice of the art of. easily and.

oxidizing su lfids may be simply, readily obviated by the use of diluted oxidizing atmospheres, either of a flaming characterwhere extraneous heat is to be applied, or of a non-flaming nature where an exothermic reaction is to be restrained. F requently, atmospheres of both characteristics will be successively applied in roasting rich sulfid ores. WVi-th" rich copper glance for instance, it is desirable to start oxidation witha heat developing flaming atmosphere, continue and retar as in .pyritic smelting, a diluted non-flaming oxidizing atmosphere is usuallv alone employed, the. dilutionbeing varied inversely as the heat required; This type of atmos-fl p'here may also usefullbe employed in roasting in continuous urnaces where hot nearly finished ore advances through a draft current in the opposite direction, and also in certain roasting operations where the draft current is employed hot; The diluted flaming atmosphere is also useful alone, particularly in the case of poor ores and such as need extraneous heat.

While any indifferent gas would answeras a diluent in-maik'ing the diluted atmosphere employed,.-in practice I prefer to use products of combustiom-either from a fuel burning furnace or from the. ore furnace itself. 7

The latter have preferable characteristics in For 'ble develops no less certain relations, hereinafter pointed out; the former in certain other relations; but generallv they are more or less interchange? able. Where the diluted atmosphere is to have flaming, or heat evolving charactcristics, itis to be mixed with a modicum of combustible gas. Such an atmosphere, for instance, maybe produced by a mixture of any combustible gas with an excess of air over that necessary to burn it and with more or less productsof combustion. The latter constituent acts'toretard combustion both by virtue of the simple dilution and also by reason of the laws of massactiol'i; the tendency which .carbon dioxid exercises to restrain the formation of more carbon dioxid. Such a mixture may be made as tardily burning as desired; 2'. 6., while its combustitotal heat in burning thanit would in a concentrated condition, the evolution is'extended over a larger area and a greater time; area and time being controllable overindefinitely wide limits. In

other words, such a flame may be made of' oxidizing any temperature desired. Its power is controllable by regulating the amountof gases and neutral diluent used. Obviously, either may be controlled by manipulating a valve or two, changing the proportions of the constituents of the mixture. Such a mixture may be made by admixing the three constituents direct in such proportions as the needs of the moment may require. In making the mixture of air and diluentand combustible, it is in general advisable, to avoid explosion and the necessity of elaborate apparatus, to admix the comv bustible gas and the products of combustion prior to admixing the air. exigencies of the roasting or oxidizing operation will require changes of proportions of the constituents of the draft current continuously.

Commonly, the

The flaming atmosphere may, very advantageously, be made from solid fuel by the simple expedient of forcing a draft of controlled proportions of air and products of lot combustion through a bed of ignited fuel at I a rate faster than the fuelcan react therewith. The result is a tardily burning gas mixture consisting of carbon monoxid from the fuel, excess of carbon dioxid and nitrogen from the products of combustion and of the excess of air. The air is distributed throughout the entire eflluent gas mass in thorough admixture with the combustible gas (CO) but combustion is slackened by the diluent nitrogen and carbon dioxid, the latter having also a chemical restraining influence over the velocity of combustion. Combustion is not ordinarily completed till the gas mass comes into proximity to the heat radiating walls of. a furnace chamber. In another jlPpllCfitlOIl pending concurrently herewith and now matured into Patent No.

esa'gse 819,045, May 1,1906, Ihave describediand claimed the art of heatingireverberatoryfurnaces by a tardily burning gas mass of this character. In the "present invent on, however, I preferably use a somewhat different' gas mass, carrying more'oxygen, as I design it for oxidizing purposesprimarily rather than-simple heating, and less combustible gas. As the active'retarding agent iniprodnets of combustion from fuel used for dilatf ing fiaminggas masses ofithecharacter described is carbon"cl i( )xid',.in cases where a larger amount of carbon-dioxid is required 1, than is given off byfuel, the waste gasesfrom cement or lime kilns, or other calciningfurnaces which containmoreof this body than ordinary fuel ga'sespmay beusefully' employed. This operation both in thepatented process and in that herein described result in an admixture of unchanged air,

nitrogen, carbon monoxid from the fuel,- and unchal'iged products of combustion, as a diluent. .By differential speeding of the' draft fan and by changing the inlet valves for air and products ofcombustiomthegaseous mixture escaping from the fuel "bed may be made of: any character desired. Preferably here it is made with an excess of oxygen over the combustible, the latter usually being relatively small in amount; particularly when evolution of heat begins from-the sulfid being oxidized. l/Vhere however, the diluted atmosphere is not intended to develop heat, but to check the evolution of heat in the material beingvoxidized', the combustible gas is simplyomitted a1 d the oxidizing apparatus supplied with a'draft current of admixed air and ptroducts of combustion in controlled proportions. Intermediate dilute atmospheres mayof course be made with very small proportions of combustible. I

The products of combustion from the oxidizing furnace itself may be very usefully employed. Exactly as carbon dioxid has a specific retarding action upon the formation of more carbon dioxid, so the presence of sulfur dioxid in anoxidizing atmosphere tends to restrain the formation of moment fur dioxid from sulfur orfsulfids. There--- fore in burning-suchoreskas copperflglance or galena, by abst'ractin ing them to the airdraft current entering the furnace, combustion throughout the'masscan be retarded toany desireddegree and temperature consequently controlled with great exa'ctitude. 1 It is merely a matterofregulating the relative "proportions f of air and products of combustion. Takingadraft current of this character, if anyportion. of the roasting bed of-ore tends to local overheating, its own large development of sulfur v p a The charge having een efliuent gases from the.urnace*and returm.

furnace, I'first heat the .ame preliminarily by' means of a flame produced by a current of; mixed air, combustible gas and sufficient products of combustion to retard combustion and give a voluminous ameburning adjacent to. all parts of tle mass. draft current of this character may be pro-- 'duced either by direct admixture of the once'checks suchheating and brings it backtothegeneral avcrage'of the whole .mass-o'f ore. '-'lhis specific retarding action roasting of certain copper and silver ores,

the object is not to burn out all the sulfur from the ore. but to form sulfates, by conducting the oxidation by means of air diluted with sulfur dioxid in regulated proportions, the range oftemperature within which it is possible to carry out the reaction extended and the certainty of the operation muchcnhanced. A primary phenomeznon in the combustion offthese ores for this purpose isprobably the formation of sulfites, which are unstable compounds tending to break up, rather easily with evolution of sulfur dioxid, and the formation of sulfates is secondary; and oxidation of the sulfite. xThe presence of the sulfur dioxid 1n the oxidizing. atmosphere, however, tends to restrainthis evolution of more dioxid and to "extend the range of temperature within which the sulfites are stable. 1 Further, since the sulfates of the'heavy'meta ls have a tendency to break up with evolution of mixed oxygen andsulfur dioxid, the presence of the dioxid in the atmosphere. contributes to the stability ofthe sulfates also. use of an oxidiiing atmosphere diluted with sulfur dioxid makes easy the production of large yields, even upto theory, 'n the case of copper, zinc, silver, nickel, obalt, etc., sulfates. 1n the case of the co per sulfate,

this process is very advantageous as cheap-' ening the cost of bluestone, and it is also advantageous as a preliminary to electrolytic processes. The formation of silver sulfate in thls'manner gives a ready and cheap method of working certain silver ores. From pure galena lead sulfate in condition for use asa pigment an be obtained readily. I

The follow ng willflserve as .a specific example'of the carryingout of my process, in the treatment of copper sulfid; it being unnecessary to illustrate particularapparatus,

as-the. apparatus may bea reverberatory or any other suitable or convenient furnace. laced within such A flaming Since the heat communicated is evolved, so

For these reasons, the' to speak, in situ, a very even heating is attained without danger of overheating, as in the use of sensible heat. As the heat of the mass gradually rises and it begins to burn, the proportion of the combustible gas in the entering draft current is gradually desulfid in the ore decreases and the heat evolution slackens. Toward the end it may even be necessary to feed in a modicum of combustible gas with the draft current.

'With a little practice, sulfids may be very exactly burned to sulfates in this manner. Further, where the eflluent ases from sulfur roasting are to be used for the production of acid, sulfurous or sulfuric, the use of draftcurren'ts containing sulfur dioxid isadvantageous as enabling the production of such effluent gases containing maximum proportions of sulfur dioxid, since the reaction can'safely be run hot and all the oxygen converted into dioxid, without danger of too violent combustion. W'here, however, the retention of some or all of the sulfur in the ore is not desirable, or where the ore is to be sweet-roasted, the use of products of combustion from ordinary coal burning furnaces, 2'. 0., the use of a gas containing carbon dioxid rather than one containing sulfur dioxid, is frequently better. dioxid has no specific retardin influence upon the evolution of sulfur dioxid and acts here. merely as a neutral or inactive diluent. Sulfur dioxid may however be usefully employed also at the stage of the operation where combustion tends.to become violent.

Use of dilute atmospheres of the character described is especially useful in treating galena. This ore is very hard to roast by the ordinary methods. Lead oxid and sulfid readily react together with production of metallic lead. Further oxid and sulfid are both readily fusible, and both tend to melt and inclose portions of unchanged ore. For these reasons, a dead-burned porous lead oxid produced from the original galena without fusion or other physical change was unknown prior to this invention. I have however discovered that this article, which is very adaptable to making lead salts and white lead, can be readily produced by my method. The galena is first heated by tardinly burning dilated flames of gas mixtures containing very little excess of oxygen until a point is reached where. it will oxidize but short of the point. where it fuses. At this stage, the combustible gas feed is discontin- Garbon ued, wholly or partially, and a draft current of mixed air and products of combustion employed. By regulation of the proportion of the components, the temperature can be kept stationary at the most desirable point. In finishing however, it is again desirable to use some small amount of combustible gas. Oxidation to sulfate should be avoided here. The lead. oxid obtained by this rocess tends to retain more or less the form 0 the original galena and is a brown red or yellow litharge. Since it is not allowed to fuse, it does not attack the furnace linings, which, however, should as a rule be of a basic nature. In finishing, if the heat be very gradually raised and a diluted atmosphere supplied containing a small proportion of combustible gas and a relatively large proportion of air, red lead may be obtained. The porosity of the unfused litharge obtained in the roasting enables oxygen to penetrate it throughout and form red lead in the maximum quantity. Ordinary litharge which has been fused in making does not oxidize nearly as readily. By this process a useful red pigment may be obtained directly from galena, and, as it still retains the porosity of the original dead-burned galena it is susceptible of very fine division and therefore possesses great covering power.

WVhile I do not regard steam as a diluent gas in the sense of the diluting gases mentioned, since it is not a gas and since it has not the specific retarding actions on the various types of combustion mentioned that.

carbon dioxid and sulfur dioxid have, yet occasionally a modicum may be used in the draft currents with advantage together with the diluent gases stated in cases where its specific chemical powers are desired, as in this method of making oxid of lead. In this process, it facilitates the decomposition of sulfite of lead ore of sulfur.

In roasting galena since the object is usually to get rid of the sulfur as quickly as po..sible, I prefer to use as the diluent gas in the draft currents mainly products of combustion from other furnaces, (carbon' dioxid waste gases) to avoid the retarding action of sulfur dioxid.

In oxidations where, as in pyritic smelting, high temperatures are desired, my process is also useful since the employment of regulated amounts of products of combustion in thedraft current supplied to the smelter enables the temperature to be regulated with an ease and certainty unknown to the usual method of working with pure air draft currents. By such use, instead of having a sudden and tumultuous heating at one stage, the heat may be evolved gradually and uniformly and thorough reaction upon-the smelting ore secured.

and therefore helps free the Any convenient form of apparatus maybe used to perform my broad process, it not! being dependent on particular structures.

Thediluted air current may be forced either over or through the mass of .ore being treated as the convenience or exigencies of the case may require In the former case,'1t

is often convenientto use furnaces of the 1 general type oflreverberatories, but,as hereinbefore stated,-thcy may with advantage be much larger than is'custom'ary 1n this art,"

the perfect control of heat, oxidation :and

other conditions affecting reactions being such that great dimensions are practicable. There not being here the fear of too-violent actlon as 1n ordinary. roasting 1n these reverberatories, draft currents may beintroducedspond with the special needs of the ore atv the point where it meets it. pThe ore may also be treated by draft currents blown through it in apparatus of the general type of converters. In treating lead and similar ores to prepare them for the blast furnace, a thin layer of charcoal or" other suitable fuel may be placed in a'shallow tiltingcon-1 verter, set alight and brought to incandescencerby a blast 'ofair through twyers in the bottom and the ore fed in: above the fuel, the blast current being gradually charged with products of combustion as the ore begins to heat up. The heat maybe controlled by proper vadjustment of the composition of this diluted air blast so as to maintain the porosity of the ore until. the sulfur is burned throughout or nearly throughout the mass, but it is generally desirable for this particular purpose to. let the heat rise near the end of the burning and sinter. the ore more or less so as to agglomerate it into denser masses suited for use in the blast furnace. Of course this fusion or sintering after the bulk of the roasting is complete has not the disadvantage that sin-H tering has in thebeginning of the operation. I have described and claimed this specific process of OXldlZlng ores by blowing diluted air through the masses of the sameinxair.

other and'divisional applicatiom-Seria-l No. 300,128, filed-Feb. 8,1906... a c 1 In continuous treatment. anylre'verbera tory provided withsuitable mechanism for advancing the ore therethrough may be used. Rotary kilns, shaft-and-shelf fur-Q naces andmanyother commontypes of y t which consists 1n oxidizing such ores with metallurgical furnaces are also suitable.

lVith these structures it is. practicable and frequently desirable to introduce draft currents of different constitution" through appropriate twyers at various points in the forward progress of the ore being treated,;

the draft current at any particular point [being adapted to the needs of the ore at that point.

To recapitulate, my process, broadly, consists inoxidizmg sulfid ores by means of dlluted arr. Tlns d1lut1on may be effected partly 'wit-hcombustib1e gas and partly with products of combustion where the diluted atmosphere is intended to evolve heat or partake of the nature of flame, or the diluent maybe wholly products of combustion where checking of heat evolution in the ore is required. The products of combustion may be -either those from the burning of carbon or those from the burning of sulfur, or, and very frequently, both combined.

By'the use of this process, the roasting or oxidation of sulfids can be rushed, forced blast under relatively high pressures being applicable as there is here no fear of undue liberation of .heat or violence of reaction. Under proper control of the conditions, the oxidation can be made nearly proportional I to the amount of air delivered to the one.

:draft. carries away. the sensible heat and does not permit it to accumulate. My processtherefor not only makes possible the use of much larger apparatus than is usually,

permissible but it also, enables ores to be roasted in much shorter time than has heretofore-been practicable, thereby effecting a ,double economy. Further, since the roastinvolved in the usual operation.

What I regard as novel and desire to claim 1. The. process of treating sulfid ores which consists in oxidizing such ores with draft currents of air. diluted with controlled proportions of non-oxidizing gases. v

.2. The process of treating sulfid ores which consists in oxidizing such ores with draft, currents of air diluted'with prQducts of combustion in'controlled proportions.

3.,The process of treating sulfid ores wvhich consists in oxidizing such ores with draft currents of air diluted with controlled iproportionsof products of complete combustion and a modicum of combustible gas.

.4. The process of treating sulfid ores air. diluted with cont-rolled proportions of the products of complete combustion of carconsists in l rents of alt-Z dllute' draft currents ofair diluted with controlled proportions of combustible and inc'ombus-gi tibl e products of coinbustion of carbon;

6. The 1 process of treating sulfidores which consists in. oxidiiing a such ores" with? draft currents of diluted airf-jco'i'itairiingcontrolledproportions 'of produets' of conibus-i thermic state of th'e ore' undergoing treat ment.-;

7. The"- rocess. of treatingQ-galenawliich consists in ox'idiz'in galena'withadraft rent; of dilutedair'icon a1n1ng-control1ed-pro-' portions of. non-oxidizingidiluentf gases; X

8. The process; g t-treating galena which with? productsof complete 1 combustion ini controlled proportions-.- 9. The process of treatinggalena which consists in oxidizing 1: galena with draft currents of air diluted wit-J51 "controlled proper tions of products'of combustion and a modicum of COIHbftlStlblB gas. v

10. The 1 process of treating galena which consists .in. oxidizing galena with air diluted withcontrolled proportions of the products of combustion of carbon. p p

11. 'lhe'processof treating-galena which consists in oxidizing ga-lenawith draft cur rents of air diluted withco'ntrolled 'roportions-of combustible and incombustibie products of combustion of carb'on.

12. The process-of treating galena which consists 111' oxidizing galenalmth draft currents of diluted air and varying the dilution to correspond with the exothermic state of the ore undergoing treatment! lit-The process f-treating galena' which consists in oxidizing galcna. 'with draft currents of diluted air containing controlled proportions ofproducts' ofcombustion and combustible gas and varyingfthe' proportion of'the latter inversely to the exothermic state of the ore under oing treatment 14. The process of treating sulfid ores which consists in oxidizing'thesame with an ignited draft current of air diluted with products of-combu'stion and a modicum of combustible gas, gradually diminishing the proportion: of the.latter'asexothermic re'act1on begins, continuing the treatment with a draft current-of air and products of combus tion alone and finally finishing with a draft.

current again containing combustible gas.

15. The process of treating sulfid ores which consists in oxidizing the same with an ignited draft currentfof air diluted with products of combustion and a inodicun'iof combustible gas, gradual] y diminishing the 1 proportion of thelatter as exothermic reac- 7 tion begins, continuing the treatment witha draft current of fair and products of colnbustion alone, varying-the proport on .of the lat ter to correspond with the exothermic tcnd= .consist's*i1i oxidizinggalcna with an ignited draft current of" a11'"d1'l uted' witl1 products of combustion-nudemodicum of combustible {continuing thetrc'gatm'ent-"with a draft current of'an'" and alone;

gal'ena" with draft -curency of the" salad mass and finally finishing thezoxida'tion with a dratt'current again containin'g combustible gas.

16. lhe process of treating galcna which gas, gradually diminishing the proportion of the latter" as exothermic reaction-, l'iegins,

-products' of combustion andfinally'finishing with a draft current; 'a' in' 'containin comb'nstible gas.

1 7. he processo treatinggalena which consistsin oxidizing the same with an ignited so draft current of air diluted with products of combustionand'amodicum of coinbustible gas; gradually diminishing the proportion-ofthe latter as 'exothermic reaction bcgins; continuing, the treatment with a draft current- 0f air and products of combustion alone, varying the proportion of the latter 'tocorrespond with the exothermic tendency *of the *sulfid mass, and-finally oxidation with'a draft: current again confinishing the tainlng combustible gas.-- I

18. The; process of treating sulfid ores which consists: in maintaining the 7 same above; the temperature necessary for oxidationbut below that'necessary for fusion in 5 a-d-iluted air current containin controlled proportions of diluent non-oxi "izing gases.

19. The process of treating galena which oonsists'in maintaining-thesame above the temperature necessary for oxidation but bc- 10o low that necessary for fusion in a diluted air current containing controlled proportions of diluent non-oxidizing gases.

20. The process of treating sulfid ores which consists in maintaining the same above the temperature necessary for oxidation but below that necessary for fusion in an air current containing controlled proportions of products of combustion.

21. The process of treating galena which consists in maintainingthe same above the temperature necessary for oxidation but below that necessary for fusion in an air current containingproducts of combustion.

22. Theproccss of checking undue evolution of; heat in theb11rningof sulfid ores which consists incontinuouslydiluting the oxidizingaircurrent by varying amounts ofproducts vofcombustion corresponding to the exothermic tendcncy of the mass of ore un- 'dertreatnient.

23'. The process of checking undue evolution of'heat in the burning of galena which consists in continuously diluting the oxidizing'air currentby \-'arying amounts of prodi2..- ucts Of'COlIlbllSilOll corresponding to the exoth'ernnc tendency of the ore under treatment.

2st. The process of oxidizing sultid ores which consists in passing over an ignited mu mass of such ore a draft current of diluted air containing controlled proportions of air.

25. The process of oxidizing galena which consists in passing over an ignited mass of galena a draft current of diluted air containing controlled proportions of air.

26. The continuous process of oxidizing sulfid ores which consists in passing a continuous current of such ore against a draft currentof diluted air containing controlled proportions of air.

2'1 The continuous process of oxidizing sulfid ores which consists in passing a continuous current of such ore against a plurality 6f draft currents of difierent constitution, one or more ofsaid draft currents being diluted air containing controlled proportions of air.

28. The continuous process of oxidizing ga'lena which consists in passing a continu- I ous current of such ore against adraftcurrent of diluted air containing controlled proportions of air.

29. The continuous process of oxidizing galena which consists in passing a continuous current of such ore against a plurality of draft currents of different constitution, one or more of said draft currents being diluted air containing controlled proportions 0 air.

In testimony whereof I aflix my signature,

in the presence of two witnesses.

BYRON E. ELDRED.

Witnesses:

K. P. MoELRoY,- A. M. SENIOR. 

